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Thread: New house: Question about long lag until hot water and use of circulator

  1. #16

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    Quote Originally Posted by leejosepho View Post
    Do you recall whether the article mentioned anything about a check valve? Without one, I believe the recirc line could run backwards and deliver tepid water to the faucet. I have a swing-check valve in my own pumped recirc line to be sure that does not happen.

    I do not recall mention of a check valve in the article, it was a long time ago. I did a search on the word "gravity" here and found another thread on this topic. A check valve was mentioned. Cannot use a spring loaded check valve, has to be a flap type. Alos talked about drilling a small hole in the flap ..... I got lost after that.

    My problem is that the last 7 feet of the pipe run at the far end is in a very cold unheated underside of an enclosed porch with minimal insulation and plenty of air leak. I don't know if the gravity system will work. I suppose the downward force of the return water have to overcome any downward force in the supply pipe. In my case, the supply pipe water will get colder and colder as it move toward the far end. At what point, when the water gets cold enough, will it exert a backward force IN THE SUPPLY PIPE? Will this force be overcome by the force in the return pipe? A check valve may prevent backward flow but it won't help if the water don't move either.

  2. #17

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    Just thought of something. It SHOULD work. Even though the far end, last 7 feet or so is in a cold environment, both the supply and the return pipe is in the same environment. So they will have equal forces on that section and they SHOULD cancel out. The temperature differential at the rest of the pipes will drive the passive circulation. Make sense?

  3. #18
    Retired Defense Industry Engineer jadnashua's Avatar
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    Running hot water lines through an unheated area, then adding recirculation will add a lot of cost to the operation. You really need to insulate both the supply and return lines.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #19
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by xroad View Post
    Just thought of something ...
    The temperature differential at the rest of the pipes will drive the passive circulation. Make sense?
    I would say that is likely, but I do not know for sure.

    I used to live in a large and poorly-insulated house with a large coal furnace that had been converted to gas but was still dependent upon convection (no forced air). The gas bill there was atrocious, but the house did stay sufficiently warm ... and my point here is this: Natural convection or "gravity flow", at least as I know it, for anything related to heating is far from efficient. So yes, your line might stay warm that way, but you will likely need a circulation pump if you want truly-hot water quickly available at the tap.

  5. #20
    Moderator & Master Plumber hj's Avatar
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    Gravity circulation will work great, UNTIL the first place the pipes turn downward, such as a jog under a beam in a basement, or going into the concrete floor. A gravity system either has to be designed for it, OR the installer has to have a lot of luck so it happens accidentally.

  6. #21

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    Quote Originally Posted by leejosepho View Post
    Natural convection or "gravity flow", at least as I know it, for anything related to heating is far from efficient. So yes, your line might stay warm that way, but you will likely need a circulation pump if you want truly-hot water quickly available at the tap.
    It makes sense, all my mental excercise is just a technical discussion. I cannot act on speculation. The water tends to move slow. Routed through an unheated space, even with pipe insulatioin, will probably have so much heat loss that it won't do any good. It will change the situation to really-really cold water for a few minutes to very cold water for a few minutes.

  7. #22

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    Quote Originally Posted by hj View Post
    Gravity circulation will work great, UNTIL the first place the pipes turn downward, such as a jog under a beam in a basement, or going into the concrete floor.
    What do you mean with that statement? Please clarify/educate.

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